OS 10.4 - Quick Dock Question

Just abandonded my DELL for my first Mac, a 15 inch PowerBook G4, which (on the whole) is fantastic.

Quick question. I used to have an icon on my dock, just left of the trash can, that was silver with an '@' symbol on the top. I have just accidentally dropped this onto the desktop, which is obviously a delete command in OS X (complete with smoke effects!!).